TypeError: expected bytes, not str

import base64
import io
a = ""
b = base64.b64encode(bytes(a,'gb2312')) # 对字符串编码  URLError(ConnectionRefusedError(10061, '由于目标计算机积极拒绝，无法连接。', None, 10061),) this is a test   
print ('b11:',b)
print ('b12:',base64.b64decode(b) )# 对字符串解码
c = io.StringIO()
c.write(a)
d = io.StringIO()
e = io.StringIO()
c.seek(0)
print(c, d)
#s1=str(c)
print(type(c))
base64.b64encode(bytes(str(c),'gb2312'))# 对StringIO内的数据进行编码
print (d.getvalue())
d.seek(0)
base64.decode(d, e) # 对StringIO内的数据进行解码
print (e.getvalue())
a = "this is a +test"
b = base64.urlsafe_b64encode(a) # 进行url的字符串编码

运行代码后后，b = base64.urlsafe_b64encode(a)处报错 TypeError: expected bytes, not str

代码修改如下：

import base64
import io
a = ""
b = base64.b64encode(bytes(a,'gb2312')) # 对字符串编码  URLError(ConnectionRefusedError(10061, '由于目标计算机积极拒绝，无法连接。', None, 10061),) this is a test   
print ('b11:',b)
print ('b12:',base64.b64decode(b) )# 对字符串解码
c = io.StringIO()
c.write(a)
d = io.StringIO()
e = io.StringIO()
c.seek(0)
print(c, d)
#s1=str(c)
print(type(c))
base64.b64encode(bytes(str(c),'gb2312'))# 对StringIO内的数据进行编码
print (d.getvalue())
d.seek(0)
base64.decode(d, e) # 对StringIO内的数据进行解码
print (e.getvalue())
a = "this is a +test"

b = base64.urlsafe_b64encode(bytes(a,'gb2312'))